Pressure actuated switch and method for making same

ABSTRACT

A pressure actuated or responsive switch having a predetermined level of sensitivity. The switch includes a pair of flat contacts with a layer of resilient, non-electrically conducting, porous material sandwiched therebetween for normally holding said contact in spaced apart relation. The size of the openings formed in the porous material is sufficiently large to prevent complete closure thereof when said porous material is compressed by a force in a direction generally normal to the plane in which said material is disposed. The switch contacts are preferably formed from a flexible screen material. The switch contacts are enclosed in a fluid tight chamber by sealing a flexible, heat softenable, electrically non-conducting layer of material to the base or support member while simultaneously applying tension to the flexible layer of material. The sensitivity of the switch is adjusted to a predetermined level by applying heat to the flexible layer of material and simultaneously reducing pressure within the fluid tight chamber below the ambient pressure thereby relieving local stress concentrations contained within the flexible layer of material as a result of applying tension thereto during the sealing step. The sensitivity of the pressure actuated switch is further controlled by controlling the pressure within the fluid tight chamber.

United States Patent 11 1 Brown et al. I

[ Nov. 18, 1975 [54] PRESSURE ACTUATED SWITCH AND METHOD FOR MAKING SAME [75] Inventors: David F. Brown, Greeley, Colo.;

Harold C. Urban, West Lake, Ohio [73] Assignee: Colorado Time Systems, Inc.,

Loveland, Colo.

[22] Filed: July 24, 1974 [21] Appl. No.: 491,366

[52] US. Cl. 200/52 R; 200/85 R 200/86 ZOO/61.43; 272/4; 340/272 [51] Int. Cl. HOIH 35/00 [58] Field of Search 200/85, 61.43, 86, 52 R;

[56] References Cited UNITED STATES PATENTS 1,776,992 9/1930 Brockman 200/86 R' 3,l65,606 l/l965 Cooper ZOO/86R 3,188,422 6/1965 Wilcox 200/86 R 1 3,745,275 7/1973 Degiez 200/52 R 3,784,768 1/1974 Hunt 200/52 R Primary ExaminerDavid Smith, Jr. Attorney, Agent, or Firm-Burton, Crandell & Polumbus [57] ABSTRACT A pressure actuated or responsive switch having a predetermined level of sensitivity. The switch includes a pair of flat contacts with a layer of resilient, nonelectrically conducting, porous material sandwiched therebetween for normally holding said contact in spaced apartrelation. The size of the openings formed in the porous material is sufficiently large to prevent complete closure thereof when said porous material is compressed by a force in a direction generally normal to the plane in which said material is disposed. The

switch contacts are preferably formed from a flexible screen material. The switch contacts are enclosed in a fluid tight chamber by sealing a flexible, heat softenable, electrically non-conducting layer of material to the base or support member while simultaneously applying tension to the flexible layer of material. The Sensitivity of the switch is adjusted to a predetermined level by applying heat to the flexible layer of material and simultaneously reducing pressure within the fluid tight chamber below the ambient pressure thereby relieving local stress concentrations contained within the flexible layer of material as a result of applying tension thereto during the sealing step. The sensitivity of the pressure actuated switch is further controlled by controlling the pressure within the fluid tight chamber.

20 Claims, 7 Drawing Figures US. Patent Nov. 18, 1975 Fig PRESSURE ACTUATED SWITCH AND METHOD FOR MAKING SAME BACKGROUND OF THE INVENTION A Heretofore, many pressure actuated or pressureresponsive switches have been proposed or built. lllustrative prior art switches are shown in US. Pat. Nos. 2,700,080, 3,056,005, 3,230,325, 3,243,540, 3,396,252, 3,436,504, 3,522,398, 3,584,169 and 3,784,768. Known prior art pressure responsive switches have proven to be disadvantageous in certain applications for various reasons. For example, said prior art switches were limited in some applications since same could not be activated by applying a force over a small localized area since the insulating layer of material disposed between the switch contacts prevented one of said contacts from physically engaging the other one of said contacts. Additionally, the sensitivity of known prior art switches could not be controlled or adjusted to a predetermined level. Moreover, some prior art switches were so sensitive that same would be actuated either through the application of a force over a small localized area or the application of a force over a relatively largesurface area. Also, other prior art pressure actuated switches were expensive to construct or had a relatively short life.

The pressure actuated or responsive switch of this invention overcomes the disadvantages referred to above by providing a switch which is inexpensive to manufacture, has a relatively long operating life, can be used in an environment where said switch is subjected to a pressure loading over a large surface thereof without actuating same and yet which is actuatable when subjected to a force over a small localized area, and the sensitivity thereof may be set to a predetermined level and may subsequently be adjusted to a different level if desired or required.

SUMMARY OF THE INVENTION The pressure actuated switch of this invention comprises a rigid, flat, non-electrically conducting base member, a pair of flat, electrically conducting switch contacts having a layer of resilient, non-electrically conducting, porous material sandwiched between said switch contacts wherein said porous material normally holds said switch contacts in spaced apart relation. Said porous material is yieldably compressible and yet, following removal of said compressive force, returns to its original configuration. The size of the openings formed in said porous material is sufficiently large to provide a plurality of openings through said layer when said porous material is subjected to a force in a direction generally normal to a plane in which said material is disposed. The switch also includes a non-electrically conducting, flexible layer of material cooperating with the base member for forming a chamber in which is disposed said switch contacts, means for sealing said chamber to effect a fluid tight chamber, and a pair of electrical conductors each of which isattached to a respective one of said switch contacts and extends exteriorly of said chamber. The switch may also include means for effecting fluid communication between said chamber and the ambient environment whereby the pressure maintained within said chamber may be controlled.

The method of this invention comprises selecting a layer of resilient, electrically non-conducting, porous material which is yieldably compressible and returns to its original configuration following the removal of the force producing compression and which has pore openings throughout of sufficient size such that, upon application of a compressible force in a direction generally normal to a plane in which is disposed said porous material at any point on the surface thereof, the pore openings disposed beneath the application of said force do not completely close, mounting said layer of porous material between a large, flat, electrically conducting flexible screen member and a large, flat, electrically conducting member to form an assembly of switch contacts, mounting said assembled switch contacts on a rigid support member with one surface of said large, flat electrically conducting member being disposed in contact with said support member, attaching to each of said electrically conducting members a respective one of a pair of electrical conduits, enclosing said assembled switch contacts in a portion of said attached electrical conduits in a fluid tight chamber by sealing the flexible, heat softenable, electrically non-conducting layer of material to said support member while simultaneously applying tension to said flexible layer of material, and adjusting the sensitivity of the switch by applying heat to said flexible layer of material and simultaneously reducing the pressure within said chamber below the ambient pressure thereby relieving local stress concentrations contained within said flexible layer of material as a result of the application of a tension thereto during the sealing step.

A primary object of this invention is to provide a new and novel pressure actuated switch having a controllable level of sensitivity.

Another object of this invention is to provide a pressure actuated switch as aforedescribed in which the switch contacts thereof are formed from a screen material.

Another object of this invention is to provide a pressure actuated switch as aforedescribed in which the mesh size of one screen member differs from the mesh size of the other screen member and the size of openings formed in the layer of porous material varies between the mesh sizes of said screen members.

Another object of this invention is to provide a pressure actuated switch as aforedescribed in which the size of openings of the switch contact disposed against a surface of the rigid base member is smaller than the size of openings of the other switch contact, and the size of openings formed in said layer of porous material varies between the sizes of the openings of said switch contacts.

Another object of this invention is to provide a pressure actuated switch as aforedescribed in which the size of openings of the screen member disposed against a surface of the base member varies down to a mesh size of approximately 32 and the size of openings of the flexible screen member varies up to a mesh size of approximately 18.

Another object of this invention is to provide a pressure actuated switch as aforedescribed including means for securing the edges of the electrically conducting members relative to the base member to permit thermal expansion of the base member relative to the thermal expansion of the electrically conducting members without appreciably changing the sensitivity of the pressure actuated switch.

Another object of this invention is to provide a pressure actuated switch as aforedescribed in which the layer of porous material is formed from a polyurethane foam.

Another object of this invention is to provide a pressure actuated switch as aforedescribed which may be used at the end of a swimming lane in a swimming pool for the purpose of sensing when a swimmer has reached the end of a swimming lane and yet which is not actuated by the varying pressure associated with water waves found in a swimming pool.

Another object of this invention is to provide a system for sensing when a swimmer has reached the end of a swimming lane in a swimming pool wherein the end of the swimming lane includes a vertically extending surface, said system comprising a generally flat, pressure actuated switch as aforedescribed, and a pressure actuated tape switch mounted within said fluid tight chamber of said pressure actuated switch along the upper part thereof.

Another object of this invention is to provide a method of constructing a pressure actuated switch as aforedescribed including the step of further adjusting the sensitivity of said switch by controlling the pressure within said fluid tight chamber.

Other objects and features of this invention will become apparent by reference to the following specification and to the drawings.

IN THE DRAWINGS FIG. 1 is a perspective view of a pressure actuated switch constructed in accordance with this invention and mounted at one end of a swimming lane in a swimming pool;

FIG. 2 is a front elevational view of the pressure actuated switch shown in FIG. 1;

FIG. 3 is a cross-sectional view taken along line 33 of FIG. 2;

FIG. 4 is a cross-sectional view taken along line 4-4 of FIG. 2;

FIG. 5 is a cross-sectional view taken along line 5-5 of FIG. 4;

FIG. 6 is across-sectional view of a portion of the pressure actuated switch constructed in accordance with this invention showing the position of the various parts when subjected to an actuating force; and

FIG. 7 is an exposed view showing the attachment of the switch contacts to the base or support member to permit relative thermal expansion of said base or support member in the switch contacts.

DESCRIPTION OF THE PREFERRED EMBODIMENT The pressure actuated switch of this invention is especially adapted for use at the end of a swimming lane in a swimming pool for the purpose of sensing when a swimmer has reached the end of a swimming pool as a result of the swimmer actually contacting a portion of said switch. The pressure actuated switch of this invention is sensitive to the touching thereof by a swimmer and yet is insensitive to pressures generated by water wave action. The pressure actuated switch of this invention is compact in construction and has a depth of less than one-half of an inch. Construction of a pressure actuated switch having a shallow depth is important since swimming lanes used for competitive swimming must be accurate within plus one-half inch. The pressure actuated switch of this invention is sensitive enough to register a contacting thereof by a swimmer and yet resists a firm hard force being applied thereto such as occurs during a' kick turn. Said switch is safe for use in a swimming pool since it has no cutting edges or sharp corners and yet is sufficiently dense to prevent wafting or floating in heavy water currents.

Referring now to the drawings, a pressure actuated switch 12 is shown in FIG. 1 as being mounted at the end of a swimming lane in a swimming pool. Conventionally, in swimming pools a black stripe 14 extends longitudinally of each swimming lane to identify said swimminglane. The outer surface of the pressure actuated switch shown in FIG. 1 has a coating 16 which represents the continuation of the black stripe 14 normally found in swimming lanes in a swimming pool. Preferably, the entire vertical surface of the pressure actuated switch 12 shown in FIG. 1 is coated with a non-skid material to assist the swimmer in effecting a quick kick turn without having his foot slip against the end of the swimming lane.

The pressure actuated switch 12 of this invention comprises a rigid, flat base or support member 18, see FIGS. 3, 6 and 7, a first flat, electrically conducting member 20, a second flat flexible screen member 22, a layer of resilient, non-electrically conducting porous material 24, a flexible, non-electrically conducting, heat softenable layer of material 26, a pair of electrical conductors 28 each of which is attached to a respective one of said electrically conducting members, and means 30 for effecting fluid communication with the interior and exterior of the pressure actuated switch. The first flat, electrically conducting member 20 is preferably formed from a screen material. The layer 24 of porous material holds the electrically conducting members 20 and 22 in normally spaced apart relationship. The layer 24 of porous material is yieldably compressible when subjected to a force in a direction generally normal to a plane in which said porous material is disposed and, upon removal of said compressive force, returns to its original configuration. The size of the openings formed in said porous material is sufficiently large to prevent complete closure thereof when said porous material is subjected to a force sufficient to permit one of the electrically conducting members to contact the other member. It has been found that the layer 24 of porous material may be formed from a reticulated polyurethane industrial foam manufactured by Scott Paper Company and having approximately 30 pores per inch and being about one-eighth inch in thickness.

Where the switch contacts or electrically conducting members 20 and 22 are formed from screen material, the mesh size of one of the screen members preferably differs from the mesh size of the other screen member and the size of the openings formed in the layer 24 of porous material varies between the mesh sizes of said screen members 20 and 22. Preferably, a coarser screen materialis used to form the electrically conducting member 20 than is used to form the flexible screen member 22. It has been found that the size of the openings of the flexible screen member 22 may vary up to a mesh size of approximately 18 and the size of the openings of the first electrically conducting member 20 may vary down to a mesh size of approximately 32. Since the flexible screen member 22 must move toward and contact the electrically conducting member 20 in order to actuate the switch of this invention, it is preferable that the screen member 22 be more flexible in character than the screen member used to form electrically conducting member 20. This relationship is accurately illustrated in FIG. 7 while members and 22 are schematically shown in FIGS. 3 and 6.

The rigid base or support member 18 may be constructed from any one of various materials, however, it has been found that a rigid polyvinyl chloride material is particularly suited for a pressure actuated switch constructed for use in a swimming pool application.

The flexible layer 26 of material cooperates with the base member 18 to form a chamber in which is disposed the switch contacts. As shown in FIGS. 3 and 6, the flexible layer 26 of material is disposed against the outer surface of the flexible screen member 22. The flexible layer 26 of material is sealed to the base member 18 by any suitable means such as adhesive type A- 54l-B manufactured by the B. F. Goodrich Company. The adhesive 32 seals the layer 26 of flexible material to the base member 18 to form a fluid tight chamber. The layer 26 of flexible material is first secured to the base member 18 by the adhesive 32 along one edge thereof. A clamping force is applied along said edge until the adhesive 32 has cured or set up. Thereafter, a tension is applied to the layer 26 of flexible material as the remaining edges thereof are secured to the base member 18 through the use of the adhesive 32. Application of tension to the layer 26 of flexible material results in certain local stress concentrations being incorporated therein depending upon the configuration over which the layer 26 of flexible material passes. Tension is applied to the layer 26 of flexible material in order that said layer 26 closely adheres to the external configuration of the parts contained within the fluid tight chamber to be formed. Since local stress concentrations resulting from the application of tension as aforesaid may adversely affect the sensitivity of the pressure actuated switch for an intended application, it has been found that such tensions must be relieved wherever possible. Relieving of these tensions is effected by applying heat to the layer 26 of flexible material for the purpose of softening same. Thereafter, the layer 26 of flexible is allowed to cool and the local stress concentrations theretofore 'contained therein have been substantially relieved. Closely adhering the layer 26 of flexible material to the contour of the parts disposed within the fluid tight chamber to be formed is further achieved by reducing the level of pressure contained within the fluid tight chamber relative to the ambient .chamber existing outside of said fluid tight chamber.

Reduction of the pressure within said fluid tight chamber increases the overall sensitivity of the pressure actuated switch thereby reducing the amount of force required to actuate same. US. Pat. No. 3,548,169 may be consulted for a more detailed discussion relating to the operation and construction of an illustrative tape switch.

Reducing the amount of pressure contained within said fluid tight chamber is effected through the use of means which comprises a housing 34 having a recess 36 formed therein and a pair of fluid passageways 38 and 40 communicating with the interior of said recess 36 and the exterior of said housing 34. A self sealing rubber stopper plug 42 is mounted within fluid passageway 38. Fluid passageway 40 is connected to a fluid conduit 44 which, in turn, is connected to the interior of the fluid tight chamber. Controlling of the pressure within the fluid tight chamber is effected by inserting a hollow needle or tube (not shown) through the rubber stopper 42 and admitting or removing pressurized fluid into or out of the recess 36. When the pressure within the fluid tight chamber is reduced below that of the ambient pressure existing outside of the fluid tight chamber, a differential pressure exists across the layer 26 of flexible material thereby biasing said layer 26 of flexible material to move against the contour of the parts contained within the fluid tight chamber.

As shown in FIG. 5, the electrical wires or conduits 28 are insulated one from the other. Each of the electrical conduits 28 are connected to a respective one of the electrically conducting members 20 and 22 as aforesaid. The electrical conduits 28 pass through a plug 46 which is mounted within a housing 48. The electrical conduits 28 pass through an opening 50 formed in said housing 48 and thence into the fluid tight chamber. The housing 48 is mounted in a manner to insure a fluid tight connection between the interior of the housing 48 and the interior of the fluid tight chamber.

' In constructing the pressure actuated switch for use at the end of a swimming lane in a swimming pool for the purpose of determining when a swimmer has reached the end of a swimming lane, it has been found that the swimmer does not always contact the vertically extending surface formed at the end of the swimming lane since, sometimes, the swimmer also contacts the upper edge of the vertically extending surface formed at the end of the swimming lane. It has been found that sensing of the swimmer contacting the upper edge of the vertically extending surface formed at the end of the-swimming pool may be quickly and easily done by incorporating within the pressure actuated switch of this invention a pressure actuated tape switch 52. A longitudinally extending pressure actuated tape switch is mounted within the upper portion of the fluid tight chamber and extends along the upper surface of the vertically extending surface formed at the end of the swimming lane spaced apart therefrom. More specifically, the pressure actuated tape switch 52 is spaced apart from said surface by the approximate thickness of the base member 18. The pressure actuated tape switch 52 includes an upstanding, longitudinally extending, actuating rib portion 54. The rib portion 54 is mounted to extend generally upwardly and outwardly from the upper surface of the base member 18 to which is secured the switch contacts 20 and 22. Mounting of the pressure actuated tape switch 52 in this manner insures that some part of the swimmers hand or forearm will contact the rib portion 54 should the swimmer reach toward the edge of the pool above the upper surface thereof prior to engaging the layer 26 of flexible material disposed in contacting engagement with the outer surface of the flexible screen member 22. The pressure actuated tape switch 52 includes a pair of spaced apart electrically conducting members 56 and 58. Actuation of the tape switch 52 is effected by applying a suitable force against the rib portion 52 whereby the electrically conducting member 56 is urged downwardly into contact with the electrically conducting member 58. Where the pressure actuated tape switch 52 is mounted within the fluid tight chamber as aforesaid each of the electrical conduits 28 is connected additionally to a respective one of the electrically conducting members 56 and 58 of the pressure actuated tape switch 52. For example, one of the electrical conduits 28 would be connected to the flexible screen member 22 and theelectrically conducting member 56. The other electrical conduit 28 would be electrically connected to the member 20 and the member 58. Thus, sensing of a swimmer at the end of a swimming lane can be effected whenever member 56 of tape switch 52 contacts member 58 or member 22 contacts member 2%.

Since the thermal coefficient expansion of the material used to form the base member may differ substantially from the thermal coefficient expansion of the material used to form membeis 2d and 22, it has been found that the sensitivity of a pressure actuated switch constructed in accordance with the subject invention will be affected by a temperature change. A change in the sensitivity of the pressure actuated switch may be avoided by securing the members 20 and 22 relative to the base member 18 and the layer 26 of flexible material by the use of strips of double sided adhesive tape 60, 62 and 64. Said strips of tape dd, 62, and 64 permit movement of the materials relative to each other thereby preventing stress concentrations from being incorporated within base parts of the pressure actuated switch which would adversely effect the overall sensitivity thereof. it has been found desirable to use a strip of material (66 between the member 20 and the layer 2d of porous material, see FIG. 7, in lieu of a strip of double sided adhesive tape. The strip 66 of material is adhesively coated on the lower surface. Strip 66 must be more resistent to puncture than the strips 6%, 62 and 64 where ends of a wire screen are involved since otherwise a fluid tight chamber might not be effected.

In view of the foregoing, it will be recognized that a new and novel pressure actuated switch and a method of making same has been descr ed. Further, it will be recognized that the pressure actuated switch of this invention is inexpensive to manufach. e, may be adjusted over a wide range of sensitivity, am' does not require any precision machining or critically positioning of the various parts. The pressure actuated switch made for use at the end of a swimming lane in a swimming pool is relatively light weight, weighing approximately pounds, and may be easily handled by a single persor It has been found that for a conventional swimming lane, a switch contact area of 57 inch wide by l'7 /zinch high is adequate. As shown in H6. l and 3, the base member is preferably formed with a horizontal portion 18a for engaging the horizontal surface 68 extending about the edge of the pool. Suitable means (not shown) may be formed or attached to the undersurface of por tion 18a for securing said switch E2 to the side of the swimming pool.

The use of a layer of porous material as aforedescribed which has a large number of openings formed therethrough wherein each opening is separated from another opening by a narrow web of material, i.e., less than one-tenth the diameter of the opening, enables the construction of a pressure actuated switch having the advantages as described above. For example, it will be noted that the switch contacts can be caused to engage each other over the entire surface thereof due to the use of the porous layer of material as aforesaid. This is different from many of the prior art switches which used a layer of material having a plurality of apertures the switch contacts immediately above one of the interformed therethrough with a relatively wide strip con- H connecting strips, no electrical contact would be obtained. I I i in light of the foregoing, it will be understood that a pressure actuatedswitch of fairlyunifonn sensitivity is obtained where the contours one screen member. said contours being takeriin cross-section fors'aid screen member, diffr' from the contours of the other screen member. This is achievedwhere the size of the openings of one screen member, such as screen member 22,

is larger than the size of the opening of the other screen member, i.e., screen member 2d.

It will be apparent to those skilled in the art that the disclosed switch and method for making same may be modified; therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.

We claim:

1. A generally flat, pressure actuated. cor iris ing:

a. a rigid, flat base member,

b. a first flat screen member is;

cally conducting material and is surface of said base member,

c. a second flat flexible screen member formed from an electrically conducting material,

. a layer of resilient, porous material formed from non-electrically conducting material, said porous material being disposed intermediate said members to maintain said screen members in a normally spaced apart relationship, said porous material being yieldably compressible when subjected to a force in a direction generally normal to a plane in which is disposed said porous material whereby, upon removal of said force, said porous materia returns to its original configuration, the size of openings formed in said porous material being sufficiently large to prevent complete closure thereof when said porous material is subjected to a force in a direction generally normal to the plane in which is disposed said porous material,

e. the mesh size of one of said screen differing from the mesh size of the othe. .lll ct. member and the size of the openings formed in said layer of porous material varying between the mesh sizes of said screen members,

means securing the edges of said screen members relative to the surface of said base niernber to permit thermal expansion of said base member relative to thermal expansion of said screen members without adversely changing the sensitivity of said pressure actuated switch,

g. a flexible layer of material cooperating with said base member for forming a chamber in which is disposed said screen members and said porous layer of material, flexible layer of material being disposed against one surface of said second flexible screen member, I

h. means for sealing said chamber to effect a fluid tight chamber,

i. a pair of electricalconductors each of whichis. at-

tached to a respective one of said screen mernbers,

. said electrical conductors being. insulated one from the other and extending exterioriy of said chamber,

Clint? pp, or.

j. means for effecting fluid communication between saidchamber and exteriorly thereof for controlling the pressure within said chamber.

2. A pressure actuated switch as defined in claim 1 in which the layer of porousm aterial is formed from a polyurethane foam. d v v 3. A pressure actuated switch as defined in claim 1 in which the size of the openings of said'second flexible screen member varies up to a mesh size of approximately 18 and the size of the openings of said first screen member varies down to a mesh size of approximately 32.

4. A generally flat, pressure actuated switch comprismg:

a. a rigid, flat base member,

b. a flat member formed from an electrically conducting material and supported on one surface of said base member,

0. a flat flexible screen member formed from an electrically conducting material,

(1. a layer of resilient, porous material formed from a non-electrically conducting material, said porous material being disposed intermediate said electrically conducting members to maintain said members in a normally spaced apart relationship, said porous material'being yieldably compressible when subjected to a force in a direction generally normal to a plane in which is disposed said porous material whereby, upon removal of said force, said porous material returns to its original configuration,- the size of the openings formed in said porous material being sufficiently large to prevent complete closure thereof when said porous material is subjected to a force in a direction generally normal to the plane in which is disposed said porous material,

e. a flexible layer of material cooperating with said base member for forming a chamber in which is disposed said electrically conducting members and said porous layer of material, said flexible layer of material being disposed against one surface of said flexible screen member,

f. means for sealing said chamber to effect a fluid tight chamber, and

g. a pair of electrical conductors each of which is attached to a respective one of said electrically conducting members, said electrical conductors being insulated one from the other and extending exteriorly of said chamber.

5. A pressure actuated switch as defined in claim 4 in which said flat, electrically conducting member comprises a screen member, and said switch includes means for effecting fluid communication between said chamber and exteriorly thereof whereby the pressure maintained within said chamber may be controlled.

6. A pressure actuated switch as defined in claim 4 in which the size of the openings formed in said layer of porous material is approximately equal to the mesh size of said flexible screen member.

7. A pressure actuated switch as defined in claim in which the mesh size of one screen member differs from the mesh size of the other screen member and the size of the openings formed in said layer of porous material varies between the mesh sizes of said screen members.

8. A pressure actuated switch as defined in claim 5 in which the size of the openings of said flexible screen member is larger than the size of the openings of the other screen member, and the size of the openings formed in said layer of porous material varies between the sizes of the openings of said screen members.

9. A pressure actuated switch as defined in claim 5 in which the size of the openings of said flexible screen member varies up to a mesh size of approximately 18 and the size of the openings of the other screen member varies down to a mesh size of approximately 32. 10. A pressure actuated switch as defined in claim 4 including means for securing the edges of said electrically conducting members relative to said base member to permit thermal expansion of said base member relative to thermal expansion of said screen members without appreciably changing the sensitivity of said pressure actuated switch.

11. A pressure actuated switch as defined in claim 10 in which said securing means includes a double sided adhesive foam tape.

12. A pressure actuated switch as defined in claim 4 in which said layer of porous material is formed from a polyurethane foam.

13. In a system for sensing a swimmer has reached the end of a swimming lane in a swimming pool by physically contacting the end of said swimming lane, said end of said swimming lane including a vertically extending surface,

a. a generally flat, pressure actuated switch supported along a vertically extending surface formed across the end of a swimming lane in a swimming pool and extending substantially across said swimming lane, said switch comprising:

i. a rigid flat base member having first and second, oppositely disposed surfaces for being disposed in a generally vertical plane and an upper surface interconnecting said first and second oppositely disposed surfaces, said upper surface being constructed for disposition in a generally horizontal plane, said first surface being constructed to be mounted against a vertically extending surface formed at the end of a swimming lane in a swimming pool, said first surface being generally planar,

ii. a flat member formed from an electrically conducting material and supported on the second surface of said flat base member,

iii. a flat flexible screen member formed from an electrically conducting material,

iv. a layer of resilient, porous material formed from a non-electrically conducting material, said porous material being disposed intermediate said electrically conducting members to maintain said members in a normally spaced apart relationship, said porous material being yieldably compressible when subjected to a force in a direction generally normal to a plane in which is disposed said porous material whereby, upon removal of said force, said porous material returns to its original configuration, the size of the openings formed in said porous material being sufficiently large to prevent complete closure thereof when said porous material is subjected to a force in a direction generally normal to a plane in which is disposed said porous material,

v. a flexible layer of material cooperating with said base member for forming a chamber in which is disposed said electrically conducting members and said porous layer of material, said flexible layer of material being disposed against one surface of said flexible screen member,

vi. means for sealing said chamber to effect .a fluid tight chamber, and

vii. means for effecting fluid communication between said chamber and exteriorly thereof whereby the pressure maintained within said chamber may be controlled;

b. a pressure actuated tape switch mounted within said chamber along the upper part of the second surface of said base member, said tape switch including an upstanding, longitudinally extending, actuating rib portion, said rib portion extending generally upwardly and outwardly from the second surface of said flat base member, said tape switch including a pair of normally spaced apart electrically conducting members;

c. a pair of electrical conductors each being electrically connected to a respective one of said screen members and one of said electrically conducting members of said tape switch, said electrical conductors being insulated one from the other and extending exteriorly of said chamber;

. means for sealing said chamber to effect a fluid tight chamber, and

e. means for effecting fluid communication between said chamber and exteriorly thereof whereby the pressure maintained within said chamber may be controlled.

14. ln a system as defined in claim 13 in which the flat, electrically conducting member of said pressure actuated switch comprises a screen member.

15. In a system as defined in claim 13 in which the size of the openings formed in said layer of porous material is approximately equal to the mesh size of said flexible screen member.

16. In a system as defined in claim 13 including means for securing the edges of said electrically conducting members of said pressure actuated switch relative to said base member to permit thermal expansion of said base member relative to thermal expansion of said screen members without appreciably changing the sensitivity of said pressure actuated switch.

17. In a system as defined in claim 16 in which said securing means includes a double sided adhesive foam tape.

18. In a system as defined in claim 13 in which said layer of porous material is formed from a polyurethane foam.

19. In a system as defined in claim 14 in which the size of the openings of said flexible screen member is larger than the size of the openings of the other screen member, and the size of the openings formed in said layer of porous material varies between the sizes of the openings of said screen members.

20. In a system as defined in claim 19 in which the size of the openings of said flexible screen member varies up to a mesh size of approximately 18 and the size of the opernings of the other screen member varies down to a mesh size of approximately 32. 

1. A generally flat, pressure actuated switch comprising: a. a rigid, flat base member, b. a first flat screen member formed from an electrically conducting material and supported on one surface of said base member, c. a second flat flexible screen member formed from an electrically conducting material, d. a layer of resilient, porous material formed from a nonelectrically conducting material, said porous material being disposed intermediate said screen members to maintain said screen members in a normally spaced apart relationship, said porous material being yieldably compressible when subjected to a force in a direction generally normal to a plane in which is disposed said porous material whereby, upon removal of said force, said porous material returns to its original configuration, the size of the openings formed in said porous material being sufficiently large to prevent complete closure thereof when said porous material is subjected to a force in a direction generally normal to the plane in which is disposed said porous material, e. the mesh size of one of said screen members differing from the mesh size of the other screen member and the sIze of the openings formed in said layer of porous material varying between the mesh sizes of said screen members, f. means for securing the edges of said screen members relative to the surface of said base member to permit thermal expansion of said base member relative to thermal expansion of said screen members without adversely changing the sensitivity of said pressure actuated switch, g. a flexible layer of material cooperating with said base member for forming a chamber in which is disposed said screen members and said porous layer of material, said flexible layer of material being disposed against one surface of said second flexible screen member, h. means for sealing said chamber to effect a fluid tight chamber, i. a pair of electrical conductors each of which is attached to a respective one of said screen members, said electrical conductors being insulated one from the other and extending exteriorly of said chamber, and j. means for effecting fluid communication between said chamber and exteriorly thereof for controlling the pressure within said chamber.
 2. A pressure actuated switch as defined in claim 1 in which the layer of porous material is formed from a polyurethane foam.
 3. A pressure actuated switch as defined in claim 1 in which the size of the openings of said second flexible screen member varies up to a mesh size of approximately 18 and the size of the openings of said first screen member varies down to a mesh size of approximately
 32. 4. A generally flat, pressure actuated switch comprising: a. a rigid, flat base member, b. a flat member formed from an electrically conducting material and supported on one surface of said base member, c. a flat flexible screen member formed from an electrically conducting material, d. a layer of resilient, porous material formed from a non-electrically conducting material, said porous material being disposed intermediate said electrically conducting members to maintain said members in a normally spaced apart relationship, said porous material being yieldably compressible when subjected to a force in a direction generally normal to a plane in which is disposed said porous material whereby, upon removal of said force, said porous material returns to its original configuration, the size of the openings formed in said porous material being sufficiently large to prevent complete closure thereof when said porous material is subjected to a force in a direction generally normal to the plane in which is disposed said porous material, e. a flexible layer of material cooperating with said base member for forming a chamber in which is disposed said electrically conducting members and said porous layer of material, said flexible layer of material being disposed against one surface of said flexible screen member, f. means for sealing said chamber to effect a fluid tight chamber, and g. a pair of electrical conductors each of which is attached to a respective one of said electrically conducting members, said electrical conductors being insulated one from the other and extending exteriorly of said chamber.
 5. A pressure actuated switch as defined in claim 4 in which said flat, electrically conducting member comprises a screen member, and said switch includes means for effecting fluid communication between said chamber and exteriorly thereof whereby the pressure maintained within said chamber may be controlled.
 6. A pressure actuated switch as defined in claim 4 in which the size of the openings formed in said layer of porous material is approximately equal to the mesh size of said flexible screen member.
 7. A pressure actuated switch as defined in claim 5 in which the mesh size of one screen member differs from the mesh size of the other screen member and the size of the openings formed in said layer of porous material varies between the mesh sizes of said screen members.
 8. A pressure actuated switch as defined in claim 5 in which the size of the opEnings of said flexible screen member is larger than the size of the openings of the other screen member, and the size of the openings formed in said layer of porous material varies between the sizes of the openings of said screen members.
 9. A pressure actuated switch as defined in claim 5 in which the size of the openings of said flexible screen member varies up to a mesh size of approximately 18 and the size of the openings of the other screen member varies down to a mesh size of approximately
 32. 10. A pressure actuated switch as defined in claim 4 including means for securing the edges of said electrically conducting members relative to said base member to permit thermal expansion of said base member relative to thermal expansion of said screen members without appreciably changing the sensitivity of said pressure actuated switch.
 11. A pressure actuated switch as defined in claim 10 in which said securing means includes a double sided adhesive foam tape.
 12. A pressure actuated switch as defined in claim 4 in which said layer of porous material is formed from a polyurethane foam.
 13. In a system for sensing a swimmer has reached the end of a swimming lane in a swimming pool by physically contacting the end of said swimming lane, said end of said swimming lane including a vertically extending surface, a. a generally flat, pressure actuated switch supported along a vertically extending surface formed across the end of a swimming lane in a swimming pool and extending substantially across said swimming lane, said switch comprising: i. a rigid flat base member having first and second, oppositely disposed surfaces for being disposed in a generally vertical plane and an upper surface interconnecting said first and second oppositely disposed surfaces, said upper surface being constructed for disposition in a generally horizontal plane, said first surface being constructed to be mounted against a vertically extending surface formed at the end of a swimming lane in a swimming pool, said first surface being generally planar, ii. a flat member formed from an electrically conducting material and supported on the second surface of said flat base member, iii. a flat flexible screen member formed from an electrically conducting material, iv. a layer of resilient, porous material formed from a non-electrically conducting material, said porous material being disposed intermediate said electrically conducting members to maintain said members in a normally spaced apart relationship, said porous material being yieldably compressible when subjected to a force in a direction generally normal to a plane in which is disposed said porous material whereby, upon removal of said force, said porous material returns to its original configuration, the size of the openings formed in said porous material being sufficiently large to prevent complete closure thereof when said porous material is subjected to a force in a direction generally normal to a plane in which is disposed said porous material, v. a flexible layer of material cooperating with said base member for forming a chamber in which is disposed said electrically conducting members and said porous layer of material, said flexible layer of material being disposed against one surface of said flexible screen member, vi. means for sealing said chamber to effect a fluid tight chamber, and vii. means for effecting fluid communication between said chamber and exteriorly thereof whereby the pressure maintained within said chamber may be controlled; b. a pressure actuated tape switch mounted within said chamber along the upper part of the second surface of said base member, said tape switch including an upstanding, longitudinally extending, actuating rib portion, said rib portion extending generally upwardly and outwardly from the second surface of said flat base member, said tape switch including a pair of normally spaced apart electrically conducting members; c. a pair of electrical coNductors each being electrically connected to a respective one of said screen members and one of said electrically conducting members of said tape switch, said electrical conductors being insulated one from the other and extending exteriorly of said chamber; d. means for sealing said chamber to effect a fluid tight chamber, and e. means for effecting fluid communication between said chamber and exteriorly thereof whereby the pressure maintained within said chamber may be controlled.
 14. In a system as defined in claim 13 in which the flat, electrically conducting member of said pressure actuated switch comprises a screen member.
 15. In a system as defined in claim 13 in which the size of the openings formed in said layer of porous material is approximately equal to the mesh size of said flexible screen member.
 16. In a system as defined in claim 13 including means for securing the edges of said electrically conducting members of said pressure actuated switch relative to said base member to permit thermal expansion of said base member relative to thermal expansion of said screen members without appreciably changing the sensitivity of said pressure actuated switch.
 17. In a system as defined in claim 16 in which said securing means includes a double sided adhesive foam tape.
 18. In a system as defined in claim 13 in which said layer of porous material is formed from a polyurethane foam.
 19. In a system as defined in claim 14 in which the size of the openings of said flexible screen member is larger than the size of the openings of the other screen member, and the size of the openings formed in said layer of porous material varies between the sizes of the openings of said screen members.
 20. In a system as defined in claim 19 in which the size of the openings of said flexible screen member varies up to a mesh size of approximately 18 and the size of the opernings of the other screen member varies down to a mesh size of approximately
 32. 